竖向地震动对斜坡场地非线性地震反应的影响

Effects of vertical strong ground motion on nonlinear seismic response of slope site

国内外规范中推荐或强制规定竖向地震动取为剪切反应谱的1/2～2/3,但该规定如何改进使其更合理已成为一重要课题。首先,对其研究现状简单总结,给出了可处理辐射阻尼、地震动相位特性、计算高效的二维波动显式有限元等效线性化程序 ELPSV 编制的必要性,然后进行了分析。初步研究表明,竖向地震动强度对周期在0.3 s 以下的地表剪切反应谱有一定的影响,而高于0.3 s 部分影响轻微。竖向地震动强度对斜坡场地的竖向地震反应及地表竖向反应谱影响显著,按规范的取值将偏于不安全。受地形条件影响,坡顶剪切地震反应会比坡脚反应要大,而竖向地震反应并不明显。土层边界面的地震反应要比周围反应要低,交界面效应明显。软斜坡场地地震反应特性除场地竖向地震反应自下而上先增加后减小的规律外,其他情形与硬斜坡场地的规律基本一致。该结果定量反映了竖向地震动的影响程度,为斜坡场地上考虑竖向地震动的建(构)筑结构的抗震设计提供了有益的基础。

The methods of taking half or 2/3 of shear response spectrum as vertical seismic action,recommended or prescribed compulsorily in many engineering codes at home and abroad,are used to design buildings.But how to rationally consider this effect is one of the most important tasks.Firstly,these research advancements are reviewed.The necessary of equivalent linear method of 2D wave motion explicit FEM ELPSV program with characteristic of high efficiency,real phase,actual radiation damping,is discussed.Then,strength of vertical strong ground motion influencing on response spectrum of slope site surface,equivalent response history and PGD and PGV in site section,seismic response of soft slope site are analyzed;and draw some primary conclusions as follows:There are certain influences on shear seismic response spectrum when the period less than 0.3 s,but it is very light over 0.3 s. Vertical seismic response of slope site was distinctly changed by vertical strong ground motion.Moreover,value of vertical seismic action in code for seismic design for buildings is apt to unsafety.Simultaneously,vertical response of the right site is great than the left's.The slope top's shear response is much stronger than slope feet's for slope topography condition,while vertical seismic response is not obvious.Magnified effect in strong ground motion is more than in weak motion when ratio of horizontal to vertical component(av/ah) is 2/3,which agrees with the knowledge of nonlinear response.Interestingly,Interface effects make the response is lower than ambient site response.And soft site response is essentially consistent with phenomena of the hard site,except for vertical seismic response is increased previously and then decreased from site bottom to the top.At last,concise epilogue is given.All of conclusions and study results reflected quantitatively effect extent of vertical strong ground motion,provide beneficial basement for rational considering vertical strong ground motion in aseismic design of buildings and constructions in slope site.